Transcript LHCb Physics Program

CERN Theory Institute: Flavour as a window to New Physics at the LHC: May 5 –June 13, 2008
LHCb Physics Programme
Marcel Merk
For the LHCb Collaboration
May 26, 2008
Contents:
• The LHCb Experiment
• Physics Programme:
• CP Violation
• Rare Decays
LHCb @ LHC
√s = 14 TeV
LHCb: L=2-5 x 1032 cm-2 s-1
sbb = 500 mb
sinel / s bb = 160
=> 1 “year” = 2 fb-1
b
b
b
b
LHCb
CERN
ATLAS
CMS
ALICE
A Large Hadron Collider Beauty Experiment for Precision
Measurements of CP-Violation and Rare Decays
The LHCb Detector
Muon det
Muon det
Calo’s
Calo’s
RICH-2
RICH-2
OT
OT+IT
Magnet
Magnet
RICH-1
RICH-1
VELO
VELO
31-3-2008
Installation of major structures is complete
3
A walk through the LHCb spectrometer…

4
B-Vertex Measurement
Example: Bs → Ds K
144 mm
47 mm
K
K

Bs
Ds
Primary vertex
d
s(t) ~40 fs
K
440 mm

Decay time resolution = 40 fs
Vertex Locator (Velo)
Silicon strip detector with
~ 5 mm hit resolution
 30 mm IP resolution
31-3-2008
Vertexing:
• Impact parameter trigger
• Decay distance (time) measurement
5
Momentum and Mass measurement
Momentum meas.: Mass resolution for
background suppression

6
Momentum and Mass measurement
Momentum meas.: Mass resolution for
background suppression
Mass resolution
s ~14 MeV
, K
Bs
Ds
Primary vertex

Bs→ Ds K
Bs →Ds 
K
K

bt
7
Particle Identification
RICH: K/ identification using Cherenkov light emission angle

RICH1: 5 cm aerogel n=1.03
RICH2:
100 m3 CF4 n=1.0005
4 m3 C4F10 n=1.0014
8
Particle Identification
RICH: K/ identification; eg. distinguish Ds and DsK events.
Cerenkov light emission angle
Bs → Ds K
,K
Bs
Ds
Primary vertex

K
K

KK : 97.29 ± 0.06%
K : 5.15 ± 0.02%
bt
RICH1: 5 cm aerogel n=1.03
RICH2:
100 m3 CF4 n=1.0005
4 m3 C4F10 n=1.0014
9
LHCb calorimeters
e
h

Calorimeter system :
• Identify electrons, hadrons, neutrals
• Level 0 trigger: high ET electron and hadron Primary vertex
K
Bs
Ds
bt
K
K

10
LHCb muon detection
m

Bs
Muon system:
• Level 0 trigger: High Pt muons
• Flavour tagging: eD2 = e (1-2w)2  6%
K
Ds
Primary vertex
btag
K
K

11
LHCb trigger
40 MHz
L0, HLT and L0×HLT efficiency
Detector
L0: high pT (m, e, g, h) [hardware, 4 ms]
1 MHz
HLT: high IP, high pT tracks [software]
then full reconstruction of event
HLT
rate
Storage (event size ~ 50 kB)
Event type
200 Hz Exclusive B
candidates
Physics
B (core program)
600 Hz High mass dimuons
J/, bJ/X
(unbiased)
300 Hz D* candidates
Charm (mixing & CPV)
900 Hz Inclusive b (e.g.
bm)
B (data mining)
Efficiency 
2 kHz
Note: decay time dependent
efficiency: eg. Bs → Ds K
K
Bs
Primary vertex
Ds
bt
K
K

Proper time [ps]  12
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
• Ideal measurement (no dilutions)
Bs->Ds–  (2 fb-1)
13
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
Ideal measurement (no dilutions)
+ Realistic flavour tagging dilution
Bs->Ds–  (2 fb-1)
14
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
Ideal measurement (no dilutions)
+ Realistic flavour tagging dilution
+ Realistic decay time resolution
Bs->Ds–  (2 fb-1)
15
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
Ideal measurement (no dilutions)
+ Realistic flavour tagging
+ Realistic decay time resolution
+ Background events
Bs->Ds–  (2 fb-1)
16
Measuring time dependent decays

Bs
Ds
Primary vertex
K
K

Measurement of Bs oscillations:
bt
Experimental Situation:
Ideal measurement (no dilutions)
+ Realistic flavour tagging dilution
+ Realistic decay time resolution
+ Background events
+ Trigger and selection acceptance
Bs->Ds–  (2 fb-1)
Two equally important aims for the experiment:
• Limit the dilutions: good resolution, tagging etc.
• Precise knowledge of dilutions
17
Expected Performance: GEANT MC simulation
Simulation software:
• Pythia+EvtGen
• GEANT simulation
• Detector response
Reconstruction software:
• Event Reconstruction
• Decay Selection
• Trigger/Tagging
• Physics Fitting
Used to optimise the experiment and to test physics sensitivities
18
Physics Programme
LHCb is a heavy flavour precision
experiment searching for new physics
in CP-Violation and Rare Decays
• CP Violation
• Rare Decays
19
CP Violation – LHCb Program
Bd triangle

*
V ud V ub
g
V td V
*
tb

*
V cd V cb
*
Bs triangle
V csV cb
*
V usV ub
V tsV
s
*
tb
W−
u,c,t
W−
d (s)
q
g
q
V*ib
b
Bq
W+
q
Viq
Viq
u, c,
t
u, c, t
q
W−
Bq
b
V*ib
 V ud V ub* 
g  arg  
* 
V
V
cd cb 

;
 V tsV tb* 
 s  arg  
* 
V
V
c s cb 

q1
b
b
3  ig
 1 2 / 2


A e


2
2
VC K M  

1  / 2
A



3  i d
2 i s
A

e

A

e
1


 V td V tb* 
 V cd V cb* 
  arg  
;   arg  
* 
* 
V
V
V
V
ud ub 
td tb 


q2
B d mixing phase (SM ):  d  2 
d, s
B s mixing phase (SM ):  s   2  s
CP Program: Is CKM fully consistent for trees,
boxes and penguins?
1. g measurements from trees
2. g measurement from penguins
3. s from the box: “Bs mixing phase”
4. s in penguins
20
1.a g +s from trees: Bs→DsK
• Time dependent CP violation in interference of bc and bu decays:
Bs
e
i s
Bs
e
e
Bs

i s
e
ig

i s
 i s
e
 ig
Bs e
AB/B  
Ds K
Ds K
Ds K
(
(

Bs/Bs →Ds–K+ (10 fb-1)

2
1 
1 
2

 cos  m t  2  sin ( 
cosh
t
2
Time
s
 2  cos ( s
(g
  s   sin (  m t 
 t 

 2 
( g   s   sin h 
21
Bs→DsK
• Since same topology BsDsK, Bs Ds
combine samples to fit ms, s
and Wtag together with CP phase gs.
10 fb-1 data:
Bs→ Ds-
Bs→ Ds-K+
(ms = 20)
• Use lifetime difference
s to resolve some
ambiguities (2 remain).
s(gs) = 9o–12o
Decay Time →
Channel
Yield
B/S
(2 fb-1) (90% C.L.)
BsDsK
6.2 k
[0.08-0.4]
BsDs
140 k
[0.08-0.3]
22
B →D and Bs→DsK
B  D(*) measures g in similar way as BsDsK
• More statistics, but smaller asymmetry
• No lifetime difference:
Channel
8 –fold ambiguity for g solutions
LHCb-2005-036
Yield (2 fb-1)
B/S
BsD*(K ) 
206 k
<0.3
B->D 
210 k
0.3
U-spin breaking
Invoking U-spin symmetry
(d↔s) can resolve these
ambiguities in a combined
analysis of DsK and D(*)pi
(Fleisher)
Can make an unambiguous
extraction, depending on
The value of strong phases:
s(g < 10o (in 2 fb-1)
23
1.b g from trees: B→DK
• Interfere decays bc with bu
to final states common to D0 and D0

0

A( B  D K )
 rB e

0

A( B  D K )
i B
e  ig
color
suppression
GLW method:
fD is a CP eigenstate common to
D0 and D0: fD= K+K-, +-,…
Measure: B→D0K, B → D0K, B→ D1K
• Large event rate; small interference
• Measurement rB difficult
D 0 K–
B–
rB e
i( B g

rD e
i D
fDK–
D 0 K–
ADS method:
Use common flavour state fD=(K+  –
Note: decay D0→K+– is double
Cabibbo suppressed
• Lower event rate; large interference
Decay time independent analysis
24
B→D(*)K(*)
GLW: D KK (2 rates) ;
ADS: D K
( 4 rates) ;
ADS: D K3 (4 rates) ;
(
(B
(B

  1  r  2 r cos (   g 
 ( K   K   r  ( r  2 r r cos (     g 
 ( K 3  K   r  ( r  2 r r cos (     g 
(

 B  K K




K

2
B
D





D
B

2
B
D

See talk of Angelo Carbone
B
2

D
2
B
B D
3
D
2
3
B D

B
D
B
3
D
Channel
Yield (2 fb-1)
B/S
B → D(hh) K
7.8 k
1.8
B → D(K) K , Favoured
56 k
0.6
B → D(K) K , Suppressed
0.71k
2
B → D(K3) K, Favoured
g, rB, B, D , D3
62k
0.7
B → D(K3) K, Suppressed
0.8k
2
s(g) = 5o to 13o
depending on strong
phases.
Also under study:
B± → DK± with D → Ks 
B± → DK± with D → KK 
B0 → DK*0 with D → KK, K, 
B± → D*K± with D → KK, K, 
Normalization is
arbitrary:
7 observables for 5
unknows:
s(g)
8012o
Dalitz analyses
o
18
Overall: expect precision of
6o 12o
s(g) = 5o with 2 fb-1 of data
(high background)
25
2. g from loops: B(s)→hh
See talk of
Angelo Carbone
• Interfere b u tree diagram with penguins:
A f cos  m t  A f
dir
A
CP
f
(t  
m ix
sin  m t
 t 
 t 

cosh 

A
sinh

f


 2 
 2 
• Strong parameters d (d’),  (’) are
strength and phase of penguins to tree.
Weak U-spin assumption :
d=d’+-20% , , ’ independent
• Assume mixing phases known
Channel Yield
(2 fb-1)
B/S
B
36k
0.5
BsKK
36k
0.15
Am ix  f1 ( d ,  , sin  d


Adir  f 3 ( d ',  ', sin g
KK

;
Adir  f 2 ( d ,  , sin g
;
Am ix  f 4 ( d ',  ', sin  s 


KK
BsK+K-
BG
2 fb-1
ms=20
s ( g  ~10o
Time
26
3. The Bd and Bs Mixing Phase
Time dependent CP violation in interference between mixing and decay
B
i d
e
B
0
B :
Bs
i s
e
Bs
fCP
AC P ( t )   f sin  d sin (  m d t 
N (B  J /  K S   N (B  J /  K S 
0
A CP (t ) 
Bs :
0
 f sin  s sin (  m s t 
AC P ( t ) 
cosh
“Golden mode”
s(sin2 ) ~ 0.02
  f cos  s sinh
 st
s
0
Channel

 st
2
N (B  J /  K S   N (B  J /  K S 
0
fCP
Yield
(2 fb-1)
BdJ/Ks 216 k
B/S
0.8
“Yesterday’s sensation is today’s
calibration and tomorrow’s background”
– Val Telegdi
27
Bs mixing phase
 f sin  s sin (  m s t 
AC P ( t ) 
cosh
 st
2
  f cos  s sinh
Decay
Yield
(2 fb-1)
s (s)
J/ gg
8.5 k
0.109
J/
3k
0.142
J/ ’
2.2 k
0.154
J/ ’rg
4.2 k
0.08
c 
3k
0.108
Ds+ Ds-
4k
0.133
All CP eig -
0.046
J/ 
130 k
0.023
All
-
0.021
 st
s
1. Pure CP eigenstates
Low yield, high background
2. Admixture of CP eigenstates: Bs→J/ 
“Golden mode”: Large yield, nice signature
However PS->VV requires angular analysis
to disentagle =+1 (CP-even) ,-1 (CP-odd)
28
Full 3D Angular analysis
cos   cos
cos

Study possible systematics of LHCb acceptance and reconstruction on distributions.
29
Bs→ J/ 
signal
backg
• Simultaneous likelihood analysis in
time, mass, full 3d-angular
distribution
• Include mass sidebands to model
the time spectrum and angular
distribution of the background
• Model the t resolution
 s (s)=0.02
sum
s(t)= 35 fs
time
s(M)= 14 MeV
See talk of Olivier Leroy
mass
cos
cos tr
tr
30
4.  & s from Penguins
• Compare observed phases in tree decays with those in penguins
B   K s : d
0
eff
 2
m ix
 2 s
dec ay
B s   :  s
eff
• Bs    requires time dependent CP asymmetry
(PSVV angular analysis a la J/ )
 2 s
m ix
 2 s
decay
See talk of Olivier Leroy
Channel
Yield (2 fb-1)
B/S
Weak phase precision
B  Ks
920
0.3 < B/S < 1.1
s (sin(deff)  0.23
Bs   
3.1 k
< 0.8
s (seff ) = 0.11
31
Physics Programme
LHCb is a heavy flavour precision
Experiment searching for new physics
in CP-Violation and Rare Decays
• CP Violation
• Rare Decays
32
Rare Decays – LHCb Program
Weak B-decays described by effective Hamiltonian:
H eff  
GF
2
VC K M
 C (m O
i
i
New physics shows up via new
operators Oi or modification of
Wilson coefficients Ci compared
to SM.
i
i=1,2: trees
i=3-6,8: g penguin
i=7: g penguin
i=9,10: EW penguin
Study processes that are suppressed at tree
level to look for NP affecting observables:
Branching Ratio’s, decay time asymmetries,
angular asymmetries, polarizations, …
LHCb Program: Look for deviations of the SM picture in the decays:
1. b sl+l- ; Afb(BK*mm) , B+→K+ll (RK), Bs→ mm
2. b  s g ; Acp(t) Bs g , B→K*g, Lb→Lγ, Lb→ L*γ,B →r0g, B→wγ
3. Bq l+l- ; BR (Bs mm)
4. LFV Bq l l‘ (not reported here)
33
1. B0→K*0µ+µ• Contributions from electroweak penguins
• Angular distribution is sensitive to NP
3 angles:
l,  ,K
AFB
AFB(m2μμ) theory illustration
Observable: Forward-Backward Asymmetry in l
m2mm [GeV2]
(

AF B s  m m  m  
2
NF  NB
NF  NB
Zero crossing point (so) well predicted:
S M : s 0  4.39
 0.38
 0.35
G eV
hep-ph:0106067v2
2
34
B0→K*0µ+µChannel
Yield (2 fb-1)
BG (2 fb-1)
Bs→K*m+ m–
7200+-2200 (BR)
1770+-310
Afb(s) 
Event Selection:
See talk Mitesh Patel
Remove
resonances
•AFB(s), fast MC, 2 fb2–1fb-1
s0
s(s0) = 0.5 GeV2
s = (mmm)2 [GeV2] 
Systematic study:
• Selection should not distort m2mm
• s0 point to first order not affected
35
2. Bs→g
See talk Mitesh Patel
• Probes the exclusive b →s radiative penguin
Measure time dependent CP asymmetry:
AC P
(
(t  
(B

 g    ( B
 B s  g   ( B s  g

 g

s
s

Ad ir cos  m t  Am i x sin  m t
 t 
 t 
cosh 

A
sinh




 2 
 2 
b  g (L) + (ms/mb)  g(R)
In SM b→s g is predominatly (O(ms/mb)) left handed
Observed CP violation depends on the g polarization
SM: Adir  0, Amix  sin2 sin2 , A  cos 2 cos
tan  = |b→s g R| / | b→s g L| , cos   1
Event selection:
Channel Yield
(2 fb-1)
Bs→g
11k
B/S
<0.55
Statistical precision after 2 fb-1 (1 year)
s(Adir ) = 0.11 , s (Amix ) = 0.11 (requires tagging)
s (A) = 0.22
(no tagging required)
Measures fraction “wrong” g polarization
36
3. Bs →mm
See talk Mitesh Patel
• Bs mm is helicity suppressed
SM Branching Ratio: (3.35 ± 0.32) x 10 -9
hep-ph/0604057v5
• Sensitive to NP with S or P coupling
Event Selection:
Main Backgrounds:
bm, bm
B hh
Suppressed by:
Mass & Vertex resol.
Particle Identification
Channel
SM Yield
(2 fb-1)
Background
Bs mm
30
83
With 2 fb-1 (1 “year”):
• Observe BR: 6 x 10-9 with 5 s
• Assuming SM BR: 3s observation
37
Physics Programme
LHCb is a heavy flavour precision
Experiment searching for new physics
in CP-Violation and Rare Decays
• CP Violation
• Rare Decays
+ “Other” Physics
38
“Other” Physics
See the following talks for an overview:
Raluca Muresan:
• Charm Physics: Mixing and CP Violation
Michael Schmelling:
• Non CP Violation Physics:
– B production, multiparticle production, deep inelastic scattering,
…
39
Conclusions
LHCb is a heavy flavour precision experiment searching
for New Physics in CP Violation and Rare Decays
A program to do this has been developed and the methods,
including calibrations and systematic studies, are being worked out..
CP Violation: 2 fb-1 (1 year)*
• g from trees: 5o - 10o
• g from penguins: 10o
• Bs mixing phase: 0.023
• seff from penguins: 0.11
Rare Decays: 2 fb-1 (1 year)*
• BsK*mm s0 : 0.5 GeV2
• Bs g Adir , Amix : 0.11
A
: 0.22
• Bsmm BR.: 6 x 10-9 at 5s
We appreciate the collaboration with the theory community
to continue developing new strategies.
We are excitingly looking forward to the data from the LHC.
* Expect uncertainty to scale statistically to 10 fb-1. Beyond: see Jim Libby’s talk on Upgrade
40
Backup
LHCb Detector
RICH-2 PID
MUON
ECAL
HCAL
RICH-1 PID
vertexing
Tracking (momentum)
Display of LHCb
simulated event
31-3-2008
43
Flavour Tagging
Efficiency e
Performance of flavour tagging:
Tagging power:
e D  e (1  2 w 
2
2
Bd
~50%
Bs
~50%
Wrong tag w Tagging power
33%
~6%
Full table of selections
A nnu al
sig n al
yi eld
B/ S
fro m
b b b kg .
4.8
26 k
< 0 .7
18 .5
37 k
0.3
120 .
80 k
0.3
10 .
5.4k
< 1 .0
3.4k
< 0 .5
20 .
216 k
0.8
0.16
20 .
26 k
1.0
64 .0
1.67
31 .
100 k
< 0 .3
22 .0
28 .0
0.32
31 .
20 k
0.7
65 .5
2 .0
36 .0
0.03
20 .
4.4k
< 7 .1
9 .5
86 .8
5 .0
37 .8
0.16
29 .
35 k
< 0 .7
9 .7
86 .3
7 .6
34 .3
0.22
21 .
9.3k
< 2 .4
D et .
eff.
(%)
Re c.
eff.
(%)
S el .
eff.
(%)
T ri g.
eff.
(%)
To t.
eff.
(% )
V is.
BR
(10 6 )
B0   
12 .2
91 .6
18 .3
33 .6
0.69
Bs  K K
12 .0
92 .5
28 .6
36 .7
0.99
B s  D s  
5 .4
80 .6
25 .0
31 .1
0.34
B s  D s + K 
5 .4
82 .0
20 .6
29 .5
0.27
B 0  D ~ 0 (K  )K * 0
5 .3
81 .8
22 .9
35 .4
0.35
B 0  J/ (mm ) K 0 S
6 .5
66 .5
53 .5
60 .5
1.39
B 0  J/ (ee) K 0 S
5 .8
60 .8
17 .7
26 .5
B s  J/ (mm ) 
7 .6
82 .5
41 .6
B s  J/ (ee) 
6 .7
76 .5
B0  r 
6 .0
B 0  K* 0 g
Bs   g
1.2
+ few m ore channe ls in T D R
Nominal year = 1012 bb pairs produced (107 s at L=21032 cm2s1 with sbb=500 mb)
Yields include factor 2 from CP-conjugated decays
Branching ratios from PDG or SM predictions
BsDsK 5 years data
BsDs-K+
BsDs+K-
BsbDs-K+
BsbDs+K-
Angle g in Summary